Surge Protection Devices - Single Phase and Single Pole - WHY ?

Does anyone know why you would use a 1P Surge protection device instead of a 1P+N Surge protection device which also protects Neutral

My view is that if you decided that you need to protect against surges you would always protect both wires anyway, technically if the system is grounded correctly I can see that a 1P SPD is all that is required, but I would feel better using a 1P+N all the time unless it is an end of the line cascaded SPD in a small width mini DB board (space limited) say in a hotel room or lodge chalet

They are close to the same potential until you have a lighting strike in the wrong place. Then they can be at wildly different potentials.

The ground may be bonded to the neutral however the intent is not to provide a path for surge type event such as lightning, it is to provide a path to ground in the event of a ground fault and is sized sufficiency to allow the overcurrent protection device to fault. Additionally ground conductor should be as short and straight as possible to the grounding point, it is still bonded to to the ground system but offers a more direct path. The cross sectional area or gauge of the SPD grounding conductor is determined by the type of protection desired. There are other considerations when installing SPD's which are outlined in the link below.http://www.electrical-installation.org/enwiki/Connection_of_Surge_Protection_Device

Indeed SPDs are for 2 purposes Utility Transformer Surge and Lightning surge, but I am thinking lightning here, if you use a 1P SPD (hot live only) >> are you protected at a remote outbuilding where the neutral is NOT bonded to the earth ?? so in an outbuilding should you use a 1P + N (SPD) instead of a 1P SPD due to the long cable distance from the bonding point.

(Note that the remote outbuilding Earth spike is also connected to the earth spike at the central hub, through the armour on the SWA power cable that distributes power from the central hub to the remote outbuilding, so the Earth and Neutral are connected, it just happens 100 metres away hence the question about if you must use 1P+N in the outbuilding)

I also suggested that perhaps a single pole hot live T2 SPD could be used at a local room level in mini DB board, in which case it is really only acting as a 3rd in line cascaded SPD filter with 2 other SPD's above it, one at the room distribution point and one at the central hub, here cost vs large number of rooms plays a role and if it is all that is required it may be a use for a single pole SPD.

Then at the central hub, I don't think anyone wants to take any chances because this is where the inverters hang out and so a belt and braces approach is going to be the order of the day, especially when there are only a few SPD's required at the central hub.

Hence my question, why do single pole SPDs exist at all ? and has anyone used them in preference to a 1P+N device

The answer could also be that 1P+N devices are not needed at all - when earth and Neutral are bonded.So are they needed in remote outbuildings or are they just for Europe.

Say the concern is only a lightning surge coming in from somewhere upstream and getting to some in-house device. Such a surge can only come in on the hot wire (neutral is grounded at box and the transformer). So why spend extra to protect neutral?

Say the concern is only a lightning surge coming in from somewhere upstream and getting to some in-house device. Such a surge can only come in on the hot wire (neutral is grounded at box and the transformer). So why spend extra to protect neutral?

Impedence. A lightning surge is modeled electrically as a multi megahertz frequency, and will prefer a shorter path to ground - through your gear, not over a long torturous path back to your electrical panel. (typo words left out)

Note that it's not likely a SPD of any model, will preserve your gear in the case of a direct hit, but will divert the bulk of the surge into ground, sparing you a building fire from vaporizing wires inside the house. SPD's can save gear from induced voltage from near strikes.

Add genset surges which are more of a concern with uninformed users. The transfer switch getting banged back and forth in faults or doing ridiculous things and the user just watching it for hours thinking they are charging.

If you want to add a SDP to neutral go ahead and do it. It is good for the economy!

Mike, you have it reversed. A surge from upstream (as in a strike to wires between the transformer and house, NOT a direct strike on equipment in the house) WON'T come in on neutral (at the panel) keep going past the short connection to ground and take the long torturous path to your equipment. Impedance is why it won't.

An electrical engineer told me that 1P Surge protection devices are ONLY used in TN-C and TNC-S installations and using them in a TN-S system or TT system is leaving the system unprotected from surges, This is one reason why I didn't want to get into the use of these terms, because they confuse everyone. So if you are in Europe, you must use 1P+N devices for the TT earthing system.

The 1P+N device is used to manage differential voltage surges, specifically when they exist between the live and the neutral wire as shown below (left = differential voltage surge, right = normal voltage surge)The TNC-S system (once inside the in the customer premises), is used in the USA and most of the Rest of the World including the UK, South Africa, Mozambique and Australia, and I am told that 1P surge protection devices can be used in a TNC-S system, I am unsure about where you can use them and what the risks are at each type of location.

(see 3-phase TNC-S system below, the Earth and Neutral share a Common BOND in one site location ONLY and then remain Separate)

One place I can think of where 1P SPD can be used is where the Neutral and Earth are bonded which is usually the central HUB where the Solar Power and inverter room is (the one place you don't want to take any chances) so .......

in my configuration, I have an Aluminium SWA termination Gland Plate where the remote buildings come into the Solar Power room which is attached to the main load DB board. The main load DB board has earth and Neutral bonded together and they are attached to the Aluminium Gland Plate and main Earth Grid plates buried nearby the power room, so now I have a problem

I can use 1P surge devices at the bonding location but I also know that the 100 metre SWA cables are one of the most likely parts of the AC system to be affected by lightning induced AC surges so which Type 2 SPD do I use in the main load DB board. 1P or 1P+N

The electrical engineer says I don't need a 1P+N in the main load DB board because the Earth and Neutral are bonded ....Everything else is telling me to install one anyway because this is the main point of lightning entry into the system and to add a T1 device

Next question is why are their no 1P SPDs for DC boards, is that because a DC system has no wiring standard like TNC-S to reference and hence the belt and braces approach is used, hey I guess it doesn't matter, if the 1P device doesn't exist for DC then you have to use the only devices available - in this case (for DC) a device with both +VE and -VE Poles

For the very best protection, if you are home or at the site during lightning, disconnect every line that comes in from outside. Physical separation of about 8 feet is absolute best.

SPD's are for when you can't or won't do the above When the strikes get really close it does not hurt to pray.

One problem with SPD's and disconnecting is that you want to make sure the SPD is still protecting the devices or loads. I have seen installations where the equipment is not being protected because the disconnect (physical or switch) has taken it out of the circuit. This is very common when a system is made up of different makes of equipment.

Agreed - a friend had lighting jump an open transfer switch, causing significant generator damage. It didn't help that the generator may have had a better ground than other grounds with no heavy bond wire between them.

So how can one legally and easily create a very large (1+ feet) gap between building wiring and utility wiring as a storm is approaching? Wire the building like a RV with a 100A plug?

We have the correct answer from @jonr@Dave Angelini and @mike95490, Lets not forget what a SPD does, it connects Live to ground for a 1P and neutral to ground for a 1P+N for a short period to dissipate the surge by deliberately creating a Short Circuit, after the surge is dissipated, it blows a fuse (Usually a soldered joint) making the window go red and ensuring the "short circuit" is disconnected.

If neutral is already connected to ground at the bonding point, then the 1P+N at the grounding point (instead of a 1P) is a compete waste of time and money, on the DC side the same applies, however I have not seen any 1P DC devices, they all seem to be 2P = +VE and -VE, but clearly a 1P DC device is all that is needed on the main battery positive BUS in the DC board if that board has Negative connected to ground as well.

You can use an AC 1P device, remembering that DC to AC uses the voltage RMS conversion (DC is less, multiply by 0.7), so for a Negative-Earth BONDED 48V battery DC bus a USA 115V 1P AC SPD would be a better fit for purpose than a 600V 2P DC SPD, due to the much lower voltage activation point of 80V rather than 600V

Which has inspired me to think of the battery disconnect fuse holders (see picture left) which are great if you have a lot of 12V parallel battery strings say 6 where you want to be able to have an emergency disconnect as well as battery positive short circuit protection, in that case two of those fuse holders would do the trick, but for small numbers of battery strings say 1 or 2 I use the Red Dot 200 Amp BS88 Bakelite type fuse holder, where you can also pull the handle and the fast blow TF fuse out in an emergency (see picture middle and right) or for maintenance purposes to ensure the battery is disconnected before you start working.

I didn't think of using them for receiving the power cables from the combiners, it provides for solar array disconnect and lightning protection outside of the DC distribution board before passing the power onto the Outback GFDi device inside the DC distribution board, which will also trip, the charge controllers are more robust than the sensitive electronics of the inverter FET board so this should be enough protection at the charge controller end of the cable while the 150V SPD at the combiner end of the cable conducts the lightning surge to earth.

On the Schneider 600v CC's they recommend on the charger enable screen to choose disable. This gives you a way to soft start or soft stop the CC. I think you can do the same thing with the new high voltage Outback CC.